1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electronic copying machine or laser printer, which is provided with a paper feeding mechanism.
2. Description of the Related Art
In general, an image forming apparatus, such as an electronic copying machine, comprises a photoconductive drum for use as an image carrier, which is rotatably arranged substantially in the center of an apparatus housing. A developing device, transfer device, separating device, cleaner, de-electrifier, and main charger are arranged successively around the drum, thus constituting an image forming mechanism. Arranged over the image forming mechanism is an optical system, which exposes the drum to an image read from an original document, thereby forming an electrostatic latent image on the surface of the drum.
Under the image forming mechanism are arranged a paper cassette, which is stored with a number of sheets for use as record media, and a paper feeding mechanism for delivering the sheets one after another from the cassette and feeding them to the image forming mechanism. A developer image formed on the photoreceptor drum is transferred to the surface of each sheet fed by means of the paper feeding mechanism.
The paper feeding mechanism comprises a U-turn transportation path for guiding the sheets from the paper cassette to the image forming mechanism and a pickup roller for taking out the sheets from the cassette and guiding them to the transportation path. Further, feed rollers are provided in the middle of the transportation path, and an aligning roller for aligning the sheets is located at the terminal end portion of the path.
Conventionally, the pickup roller, feed rollers, and aligning roller are driven by means of one common drive motor with the aid of drive belts, gear trains, etc. These rollers must be actuated or stopped with their respective predetermined timings. To attain this, spring clutches are connected individually to the rollers, and the predetermined drive timings are obtained by on-off-controlling the clutches by means of independent control mechanisms, such as solenoids.
In the paper feeding mechanism of the conventional image forming apparatus described above, however, the spring clutches and the control mechanisms, such as the solenoids, must be provided individually for the pickup roller, feed roller, and aligning roller. Thus, the feeding mechanism requires use of many components, thereby entailing high manufacturing costs, and the whole apparatus is heavy in weight and large-sized. Moreover, a complicated control system is needed to control a lot of solenoids.